Cells must perform certain life functions to stay alive and have tiny organelles which carry out these activities. The nucleus is where the chromosomes are located. The DNA instructions are copied or transcribed by RNA and carried to the ribosomes where protein synthesis occurs, assembling new proteins that act as structural parts, or cells secretions, or whatever the cell needs to live.
Mitochondria is the powerhouse of the cell where respiration occurs providing the cell with energy to live in the form of ATP. Chloroplasts in plants allow sunlight to be captured and combined with carbon dioxide and water to form glucose, a high energy compound that provides energy.
Endoplasmic reticulum is a system of tubules for transport of necessary substances within the cell.
Lysosomes in eukaryotic cells contain enzymes to help rid the cell of old worn out organelles, to digest food, and even to break down dead cells.
Centrosomes produce the microtubules which function as a microscopic "skeleton" or framework for the cell. It also plays a role in cell division in animal cells during cell division for the formation of the spindle fibers.
Vacuoles are storage compartments in cells that store food, wastes, water and can even assist single celled organisms in locomotion.
Transport is accomplished by the plasma membrane which allows transport in and out of cells depending on size and concentration of molecules.
These are examples of how a cell stays alive.